Hi,
Since you have 1197 call/hr. That means your call arrival rate is 1197/60 (call per second)=0.3325.
The mean holding time is 60sec. So the carried traffic is
.3325*60=20Erlangs.
Look up this value in the erlang table for 1% GOS, you will get the number of trunks.
Typically for GSM air interface 2% GOS is considered. For A Interface 1%.
Regards
Arindam Dey